feat!: upgrade to prettier@3

BREAKING CHANGE: due to prettier@3 forcing downstream adoption of their
asynchronous interface, `ResultFormatter` is no longer synchronous and can now
return a `Promise`.

BREAKING CHANGE: adoption of prettier@3 requires some versions of Node to be
executed with the `--experimental-vm-modules` option. E.g.
`NODE_OPTIONS="--no-warnings --experimental-vm-modules" npx jest`.

BREAKING CHANGE: attempting to install babel-plugin-tester alongside jest@<30
will cause NPM to fail with `ERESOLVE`. This is because only jest@>=30
(jest-snapshot) supports the prettier@3 asynchronous interface.

package.json

@@ -70,7 +70,7 @@
     "core-js": "^3.33.2",
     "debug": "^4.3.4",
     "lodash.mergewith": "^4.6.2",
-    "prettier": "^2.8.3",
+    "prettier": "^3.2.4",
     "strip-indent": "^3.0.0"
   },
   "devDependencies": {
@@ -113,7 +113,7 @@
     "execa": "^5.1.1",
     "glob-gitignore": "^1.0.14",
     "husky": "^8.0.3",
-    "jest": "^29.7.0",
+    "jest": "^30.0.0-alpha.2",
     "jest-circus": "^29.7.0",
     "jest-extended": "^4.0.2",
     "lint-staged": "^15.0.2",
@@ -169,7 +169,13 @@
     "unique-filename": "^3.0.0"
   },
   "peerDependencies": {
-    "@babel/core": ">=7.11.6"
+    "@babel/core": ">=7.11.6",
+    "jest": ">=30 || >=30.0.0-alpha.2"
+  },
+  "peerDependenciesMeta": {
+    "jest": {
+      "optional": true
+    }
   },
   "engines": {
     "node": "^14.20.0 || ^16.16.0 || >=18.5.0"

src/formatters/prettier.ts

@@ -1,9 +1,9 @@
-import path from 'node:path';
 import debugFactory from 'debug';
+import path from 'node:path';
 
 import {
-  resolveConfig as resolvePrettierConfig,
   format as formatWithPrettier,
+  resolveConfig as resolvePrettierConfig,
   type Options as PrettierOptions
 } from 'prettier';
 
@@ -14,9 +14,9 @@ const debug = debugFactory('babel-plugin-tester:formatter');
 type MaybePrettierOptions = PrettierOptions | null;
 const configDirectoryCache: Record<string, MaybePrettierOptions> = Object.create(null);
 
-const getCachedConfig = (filepath: string) => {
+const getCachedConfig = async (filepath: string) => {
   if (!(filepath in configDirectoryCache)) {
-    configDirectoryCache[filepath] = resolvePrettierConfig.sync(filepath);
+    configDirectoryCache[filepath] = await resolvePrettierConfig(filepath);
     debug(
       `caching prettier configuration resolved from ${filepath}: %O`,
       configDirectoryCache[filepath]
@@ -51,7 +51,7 @@ export const prettierFormatter: ResultFormatter<{
    * @deprecated Use `prettierOptions` instead.
    */
   config: MaybePrettierOptions;
-}> = (
+}> = async (
   code,
   {
     cwd = process.cwd(),
@@ -63,15 +63,15 @@ export const prettierFormatter: ResultFormatter<{
 ) => {
   const finalPrettierOptions = {
     filepath,
-    ...prettierOptions
+    ...(await prettierOptions)
   };
 
   debug('cwd: %O', cwd);
   debug('filepath: %O', filepath);
   debug('prettier options: %O', finalPrettierOptions);
   debug('original code: %O', code);
 
-  const formattedCode = formatWithPrettier(code, finalPrettierOptions);
+  const formattedCode = await formatWithPrettier(code, finalPrettierOptions);
   debug('formatted code: %O', code);
 
   return formattedCode;

src/plugin-tester.ts

@@ -1198,7 +1198,7 @@ function pluginTester(options: PluginTesterOptions = {}) {
         // ? erroneously captured when we only really care about errors thrown by
         // ? babel
         const result = trimAndFixLineEndings(
-          formatResult(rawBabelOutput || '', {
+          await formatResult(rawBabelOutput || '', {
             cwd: formatResultFilepath ? path.dirname(formatResultFilepath) : undefined,
             filepath: formatResultFilepath,
             filename: formatResultFilepath

src/types.ts

@@ -3,10 +3,10 @@ import type { Class, Promisable } from 'type-fest';
 import type { $type } from './symbols';
 
 import type {
-  validEndOfLineValues,
-  validTitleNumberingValues,
   runPluginUnderTestHere,
-  runPresetUnderTestHere
+  runPresetUnderTestHere,
+  validEndOfLineValues,
+  validTitleNumberingValues
 } from './plugin-tester';
 
 /**
@@ -691,7 +691,7 @@ export type ResultFormatter<
      */
     filename?: string;
   } & Partial<AdditionalOptions>
-) => string;
+) => Promise<string> | string;
 
 // * The transitive dependency "pretty-format" is a dependency of Jest
 export type { Plugin as SnapshotSerializer } from 'pretty-format';